1. Field of the Invention
The present invention relates to permutation, and more particularly, to a method for generating a subframe indicating a transmission location of resource allocation information in a structure in which the resource allocation information is transmitted every subframe.
2. Discussion of the Related Art
A subframe or miniframe is used as a basic allocation unit of a downlink or uplink. A subframe or miniframe structure is used in 3rd generation partnership project (3GPP) long term evolution (LTE), ultra mobile broadband (UMB), etc. and has been discussed as one candidate in IEEE 802.16m.
FIG. 1 illustrates an example of a superframe structure.
A superframe is the largest unit comprised of a few tens of ms. The superframe refers to a resource group in the time domain from a preamble or superframe header, which is a downlink synchronization channel, to the next preamble or superframe header. The superframe is divided into frames, each of which is classified into subframes. A subframe is a basic resource allocation unit. In IEEE 802.16m, the subframe is generally comprised of 6 orthogonal frequency division multiplexing (OFDM) symbols.
In an orthogonal frequency division multiple access (OFDMA) system, a physical resource is expressed as a two-dimensional resource using a frequency resource and a time resource.
FIG. 2 illustrates an example of two-dimensional resource allocation.
The most efficient method for allocating OFDMA resources is two-dimensional allocation of the time resource and the frequency resource. However, since a location of the time resource and a location of the frequency resource are separately represented, overhead is increased.
FIG. 3 illustrates an example of one-dimensional resource allocation.
In a method for allocating resources in units of a subframe, resource allocation overhead can be reduced by providing only frequency resource indexes and allocating locations determined in units of a subframe in the time domain. Then, since resources are easily allocated, the allocation method in units of a subframe can efficiently use the resources.
A method for allocating resources within a subframe may be broadly divided into a method for allocating concatenated frequency resources and a method for distributing separated frequency resources.
The method for allocating the concatenated frequency resources is called localized permutation and is favorable when a low-speed user equipment uses adaptive modulation and coding (AMC) or beamforming/precoding. The method for distributing separated frequency resources is called distributed permutation and is favorable for a high-speed user equipment, or a user equipment which is not suitable for AMC or precoding.
Any one of the localized permutation and the distributed permutation or both of them may be used in one subframe.
Although a method using the permutation of two types can optimally configure each permutation, distribution of user equipments that prefer the permutation of two types may not coincide with a unit of a subframe.
Allocation of the permutation of two types to one subframe may be divided into two methods. First, the localized permutation is allocated first and then the distributed permutation is allocated. The second method is to allocate the distributed permutation first and then to allocate the localized permutation.
In the first method, the performance of the localized permutation is superior but the performance of the distributed permutation may be worse. On the other hand, in the second method, the performance of the distributed permutation is superior but the performance of the localized permutation may be worse. Generally, since a substantial number of user equipments prefer the localized permutation and since the performance of user equipments that prefer the localized permutation is superior to the performance of user equipments that prefer the distributed permutation, the user equipments prefer using the first method.
Resource allocation information for allocating resources in a subframe structure needs to be decoded by all user equipments or to be informed of the location of the resource allocation information. In the case where the resource allocation information should be transmitted by the distributed permutation, if the localized permutation is allocated first and then the distributed permutation is allocation, it is difficult for a user equipment to confirm which resource contains the resource allocation information.
FIG. 4 illustrates an example of a resource distribution process for allocating the localized permutation first and then allocating the distributed permutation.
A band selection resource unit (RU) refers to a physical resource of the localized permutation. Resource units except for a band selection resource unit are re-numbered (410) to configure mini-resource units and permutation is performed (420). If permutation in units of subcarriers is performed upon resources obtained by performing the permutation in units of a mini-resource unit (430), locations of resource allocation information (MAP) are determined.
Since the location of the MAP is determined after the band selection resource unit is determined, if a resource allocation method such as the location of the localized permutation is not confirmed, a user equipment cannot know the location of the resource allocation information. To solve this problem, a method may be considered for allocating the distributed permutation first and then allocating the localized permutation, thereby informing the user equipment of the location of the resource allocation information. However, since such a method affects the performance of the localized permutation, overall system performance may be deteriorated.
Meanwhile, in a method for informing a user equipment of the resource distribution method such as the localized permutation in a previous subframe, since resource allocation of a corresponding subframe should be performed in the previous subframe, the method is unfavorable in data latency. Moreover, if the user equipment has not read or could not read the resource distribution method in the previous subframe, the user equipment may not continue to read the resource allocation information.